Balers are used in agriculture to take up harvested material from a field and form it into a bale. In addition to rectangular balers in which a plunger cyclically compresses the harvested material in a baling chamber, round balers are common in which the taken-up harvested material is introduced into a cylindrical bale-forming chamber and there set into rotation by driven elements. In the case of round balers, embodiments with a fixed bale size are known in which the periphery of the bale-forming chamber is defined by rollers or rotating bodies connected rigidly to the frame of the baler, and embodiments with variable bale size in which a flexible bale forming means in the form of belts or chains equipped with catch elements define the periphery of the bale-forming chamber. The bale forming means are biased by means of a hydraulic cylinder that acts with a force on an arm carrying a roller on which the bale forming means contacts, so that the size of the bale-forming chamber grows with the taken-up quantity of material. When a specified size or density of the bale is reached, the bale is typically wound with twine, net or film and then a rear door is opened and the bale is ejected from the bale-forming chamber.
U.S. Pat. No. 5,367,865 A1 describes a round baler in which the bale-forming chamber is defined toward the front by several rollers that can be driven to rotate and that are mounted next to one another on a holder that can pivot about the rotational axis of the lowest roller. Toward the back, the bale-forming chamber is defined by a belt that revolves around several rollers. One of these rollers is mounted on the top of the holder and is not driven. Two other rollers wrapped around by belts are mounted on a first arm that can pivot about an axis and that is coupled with a second arm at which another end of the frame of the round baler attaches to a connected hydraulic cylinder used for providing a defined tensile stress in the belt. When the harvested material collects in the bale-forming chamber, the holder pivots with the rollers gradually upward about the rotational axis of the lower roller. At the same time, the belt in the rear area of the baler forms a growing loop. Because the belt is also wrapped around the roller mounted on the holder, the holder and the belt move outward in a coordinated way. Because the belt also revolves around rollers that are mounted on a rear door, the pivoting region of the first arm is sufficient for achieving a sufficient tension also when ejecting the bale.
U.S. Pat. No. 6,094,900 A1 shows a round baler wherein the bale-forming chamber is likewise defined toward the front by rollers mounted on a pivoting holder and toward the back by a belt. The holder is supported by a hydraulic cylinder relative to the frame of the baler and is furthermore extended toward the back and upward and carries, on its rear, upper end, two rollers around which the belt is wrapped. The hydraulic cylinder thus supports the holder on the frame and also defines the tensile stress of the belt. The belt also revolves around rollers mounted on a rear door, so that the pivoting region of the holder is adequate to achieve sufficient tension of the belt also when ejecting the bale.
In U.S. Pat. No. 7,165,491 B2, another round baler is described wherein the bale-forming chamber is defined only by a single bale forming means in the form of belts. The belts revolve around several deflection rollers of which a few are mounted on a first, pivoting arm and others are mounted on a second, pivoting arm. The arms are tensioned against each other by a hydraulic cylinder used for generating the desired tension in the bale forming means. The bale forming means also revolves around two deflection rollers mounted on a pivoting carrier on the bottom side of the baler. The carrier maybe pivoted about its axis extending parallel to the axis of the bale-forming chamber rearward and upward into a bale-ejection position. The two arms allow the belts to also be held sufficiently taut in the bale-ejection position of the carrier.
EP 1 308 078 A1 describes a round baler of the type mentioned above wherein the bale-forming chamber is defined toward the front by rollers that can be driven, of which one is mounted on a pivoting holder, and otherwise by a single bale forming means in the form of belts. The bale forming means revolves, among other things, around a deflection roller connected to the holder, around a deflection roller mounted on a tensioning arm, and around two deflection rollers mounted on a pivoting carrier on the bottom of the baler. The carrier can be pivoted about its axis extending parallel to the axis of the bale-forming chamber rearward and upward into a bale-ejection position. Here, a relatively long tension arm is required, in order to maintain the tension of the belt also in the bale-ejection position of the carrier.
The problem forming the basis of the invention is thus seen in providing a round baler having a mechanism that is improved relative to the state of the art for generating and maintaining the tension of the bale forming means.